1. Field of the Invention
This invention relates to a process for producing polyester side chain grafted rigid and/or semirigid chained polymers which combine with fusible polyesters to form molecularly reinforced recyclable blends which are shapable into high strength filament and fiber and also serve as compatibilizers in blends composed of a polyester matrix and rigid or semirigid chained polymers.
2. Description of the Related Art
Aliphatic-aromatic polyesters are thermoplastically shapable and are widely used for producing fiber materials, film and moldings. However, owing to their structurally and morphologically based property spectrum, these inexpensive polyesters are unsuitable for applications placing particularly high demands on strength.
True, the use of inorganic reinforcing materials, especially the use of glass fiber, makes it possible to improve the strength, rigidity and dimensional stability of polyesters, but recyclability is severely compromised as a result. Such additives make it more difficult to produce thin walled moldings and film and also to achieve impeccable surfaces, however. Wholly aromatic macromolecular polyesters generally meet the strength requirements, but are difficult to process even if, as described in DE-A 20 25 071, they are thermotropic by reason of the components used.
The addition of rigid or semirigid chained thermotropic polymers to improve the mechanical properties of matrix polymer has already been described for various polymers. According to G. Kiss [Polym. Eng. And Science 27 (1987) 6, 410-423], the use of stiff or semistiff chained thermotropic liquid crystalline polymers (LCPs) in the thermoplastic processing of polyamide and polyesters gives rise to reinforcing fibrils. The substantial incompatibility of the LCP with the polymers, however, severely limits its use. According to [EP040697A1], an improved reinforcing effect is only incompletely achievable by addition of phenoxy resins as compatibilizers.
It is common knowledge that graft copolymers are useful as compatibilizers in a large number of commercially utilized polymer blends. The main chains of these macromolecules are compatible with the polymer to be dispersed, while the side chains exhibit affinity for the matrix polymer. The effectiveness of polypropylene grafted LCP compatibilizers for in situ reinforced LCP/polypropylene blends was demonstrated by Datta et al. [Annu. Tech. conf.-Soc. Plast. Eng., 49th, 913-918]. Hökeretal. [Makromol. Chem. 190 (1989), 3295] succeeded in producing stiff chained polyarylates having high molecular weight polystyrene side chains. This improved the compatibility of the produced rod-shaped graft copolymers with polystyrene to such an extent that a homogeneous phase was formed. However, none of these graft copolymers is suitable for an adequate modification of polyesteramides.
The production and use of thermotropic polyesterimides is described by Kriecheldorf et al. [EP 0 293 713]. They are said to possess excellent processability and good mechanical properties. But their production is very cost intensive. For use as a reinforcing material in linear fusible polyesters, however, their effect is inadequate.
In DE-A 43 42 705, the compatibility of rod-shaped fusible, especially thermotropic, polymers with aliphatic or aliphatic-aromatic polyamides is improved, and a molecular reinforcement achieved, by means of polyamide side chain grafted rigid or semirigid chained polymers which bear anhydride end and/or side groups. These reactive groups are capable of reacting with the amino or amide groups of the polyamide and hence of establishing, via covalent bonds, a firm link between the thermotropic polymer and the polyamide.
This firm link is not known as a reinforcing material for linear fusible polyesters, especially for filament production. Specific applications of polyester filaments in industrial sectors and carpet manufacture require enhanced strength, modulus of elasticity and dimensional stability at elevated temperatures compared with conventional types.